1. Field of the Invention
The present invention relates to a ladder filter including a plurality of elastic wave resonators, an elastic wave filter module, and a duplexer.
2. Description of the Related Art
Conventionally, a duplexer is connected to an antenna end of mobile phones. A duplexer described in Japanese Unexamined Patent Application Publication No. 2008-67413 includes a transmission filter that is a ladder filter including a plurality of surface acoustic wave resonators. An amplifier is connected to a transmission terminal, which is an input terminal of the ladder filter. For impedance matching, a matching circuit is connected between the input terminal of the ladder filter and the amplifier. The matching circuit includes a stripline and an open stub.
Duplexers such as the one described in Japanese Unexamined Patent Application Publication No. 2008-67413 require a matching circuit to achieve impedance matching between a ladder filter and an amplifier. Thus, the dimensions of such duplexers are increased by this matching circuit.